In current Laser Activated Remote Phosphor (LARP) applications, a phosphor element may be assembled on a transparent substrate such as a heat sink. The phosphor of a LARP target is omni-directional. Accordingly, about 50% of the light may be emitted in an undesired or ‘wrong’ direction. A mirror such as a dichroic mirror may be positioned to reflect light from the excitation source back in the direction of the phosphor element.
However, not all desired light can be reflected in this manner. Depending on the incident angle of the light on the mirror, a percentage of the misdirected light may not be reflected, and is consequently wasted. In the interface area in-between the phosphor and the transparent heat sink optical filter stacks have been used. The short pass filters may be transparent for the excitation wavelength and reflective for the phosphor emission.
The present state of the LARP target leaves space for improved efficiency of the phosphor target.